1. Field of the Invention
The invention relates to an optical system, in particular an exposure lens for semiconductor lithography with a plurality of optical elements, comprising at least one load-dissipating structure, that diverts the forces originating from the optical elements, and a measuring structure which is constructed independently of said load-dissipating structure. The invention also relates to a method for changing the position of an object and/or an image in such an optical system.
2. Description of the Related Art
In optical systems that are intended to be suitable for generating optical images with a very high accuracy, for example, optical systems for very short-wave radiation such as, for example, radiation in the region of the extreme ultra violet (EUV), it must be possible to position the individual optical elements as exactly as possible with regard to their alignment in all six degrees of freedom.
For this purpose, such optical systems frequently have sensors or the like which appropriately monitor the position of the optical elements, generally mirrors in the above described case of EUV radiation, and manipulators, for the purpose of correcting or adjusting the position of the optical elements.
During operation of such optical systems, which can be exposure lenses for semiconductor lithography, for example, corresponding loads occur on the optical system itself and are absorbed in the latter by a load-dissipating structure. In addition to the static loads resulting from the weight forces of the individual components, there can also be dynamic loads in this case because of vibrations or reaction forces that occur. However, owing to the integration of the sensors in the lens itself these loads are frequently not measured, since the position of the sensors, which is always used as reference for the measurement, is also dependent on such loads.
The basic distinction between force-closed circuits and measuring circuits that on the one hand bear the load and on the other hand include the measurement are described in the specialist article entitled “Foundations of Ultraprecision Mechanism Design” by S. T. Smith and D. G. Chetwynd in “Developments in Nanotechnology” of the University of Warwick, UK, which has been published by GORDON AND BREACH SCIENCE PUBLISHERS.
The closed paths denoted in that article as measuring circuit (measurement loops) are responsible in this case for coordinating the objects to be measured and the measuring tool with one another.